Process for producing alkylaromatic compound

ABSTRACT

A process is provided for producing an alkyl aromatic compound having substituents at the 3- and 5-positions by alkylating an aromatic compound having two substituents in the meta positions with an olefin having 2 to 4 carbon atoms in the presence of a Broensted acid, followed by addition of a Lewis acid and isomerization in the copresence of the Broensted acid and the Lewis acid. According to the present invention, 3,5-dimethylethylbenzene, 3,5-dimethylcumene, etc. may be produced in a stable manner with high yield and high selectivity under mild and simple reaction conditions. The alkyl aromatic compounds having substituents at the 3- and 5-positions are useful as intermediates for functional chemicals for use in pharmaceutical, agricultural and electronic materials. With the method of the present invention, the catalyst used can be recovered and recycled. Thus, desired alkyl aromatic compounds may be obtained economically in an industrially advantageous manner while reducing the load on the environment.

TECHNICAL FIELD

The present invention relates to a process for the alkylation of anaromatic compound having substituents and, more specifically, to animproved process for producing an alkyl aromatic compound havingsubstituents at the 3- and 5-positions, such as 3,5-dimethylethylbenzeneor 3,5-dimethylcumene, by alkylating an aromatic compound having twosubstituents in the meta positions with a lower olefin such as ethyleneor propylene. Such alkyl aromatic compounds are useful as raw materialsfor pharmaceuticals, agricultural chemicals, liquid crystals, functionalpigments, solvents and monomers for engineering plastics.

BACKGROUND ART

As a method for the alkylation of an aromatic compound, a Friedel-Craftsalkylation reaction or a gaseous phase reaction which uses a solid acidcatalyst are widely known.

In alkylating an aromatic compound, the position (ortho, meta or paraposition) of the aromatic ring of the raw material to which an alkylgroup is introduced is determined by the effect of the functional group(orientation). When the desired compound is not in accord with thesubstitution orientation inherent to the functional group, however, apositional isomer of the desired compound is obtained as a product.Therefore, it is necessary to carry out disproportionation called anisomerization reaction or a transalkylation reaction in order tointroduce the alkyl group to the desired position.

For example, the Friedel-Crafts alkylation is a method known from thepast, in which a Lewis acid catalyst such as aluminum chloride is usedas a catalyst. With a method using aluminum chloride as an alkylationagent, the selectivity to a monoalkyl compound in the alkylationreaction is low. Further, the method requires complicated steps ofseparation of the monoalkylated product from a polyalkylated product bydistillation and the subsequent transalkylation of the polyalkylcompound to the monoalkyl compound (JP-A-Sho 57-40419).

JP-A-Hei 04-346939 discloses a method in which alkylation is carried outusing aluminum chloride, followed by transalkylation using a solid acidcatalyst. This method, however, requires removal or separation bydistillation of aluminum chloride and HCl used as a co-catalyst prior tothe transalkylation and, therefore, is a complicated multi-step process.

U.S. Pat. No. 5,030,777 discloses a process for producing3,5-dichloroalkylbenzene in which a dichlorobenzene is subjected to analkylation reaction using aluminum chloride as a catalyst and isopropylbromide as an alkylating agent, followed by isomeriziation andtransalkylation. This process has problems that a halogenated alkyl mustbe used as a raw material and that the process steps are complicated.

The Friedel-Crafts alkylation reaction using aluminum chloride requirescomplicated steps as described above. Further, the amount of thecatalyst relative to the raw material is large. Furthermore, thecatalyst is apt to be inactivated because the catalyst tends to form acomplex with various compounds produced by the reaction. Additionally,in order to separate the product from aluminum chloride aftertermination of the reaction, it is necessary to treat the reactionmixture with water. As a consequence of the treatment, aluminum chlorideturns into aluminum hydroxide. Thus, the method has a defect that it isdifficult to recycle the catalyst.

With regard to the alkylation reaction using other Lewis acids, U.S.Pat. No. 4,943,668 discloses an alkylation reaction of metaxylene usingaluminum halide and iodine as a catalyst and an α-olefin as analkylating agent. This method, however, has defects that iodine shouldbe used in addition to aluminum halide and that the reaction time is aslong as 2 to 7 hours. U.S. Pat. No. 4,048,248 discloses a method ofalkylating an aromatic compound using titanium tetrafluoride. With thismethod, the selectivity to the desired product is 60 to 70% and is notsatisfactory.

JP-A-Hei 06-263656 discloses a method in which a rare earth-containingcatalyst using a perfluoroalkyl group-containing sulfonyl group as acounter anion is used. This method is superior in comparison with amethod using an aluminum halide catalyst, since the catalyst may berecycled. However, this method has problems that the catalyst isexpensive and that the selectivity is low due to accompanyingpolyalkylation reaction. Namely, the yield of mono-substituted productsis about 30%, the yield of di-substituted products is about 10 to 30%,and the yield of tri-substituted products is about 10%. U.S. Pat. No.4,158,677 discloses an example of dialkylating an alkylbenzene using acarboxylic acid complex of BF₃ for the production of synthetic oils(lubricants). While the reaction gives a yield of the desired product ofas high as about 90%, this method has problems that a long reaction timeof 20 hours or more is required and that the post treatment of thereaction liquid is troublesome.

As described above, any conventional alkylation reaction using a Lewisacid as a catalyst has problems. Further, as a common problem in allmanufacturing methods, the reaction requires multi-steps and complicatedpost treatment and, therefore, is ill-suited for industrial production.

Described in the foregoing are alkylation reactions using as a catalysta Lewis acid represented by aluminum chloride. Also well known is analkylation reaction using as a catalyst HF which is a Broensted acid.Further, a reaction using HF as an alkylation catalyst is disclosed.This method pertains to a process for producing gasoline having animproved octane number, wherein C₂ to C₂₀ olefins containing HF and aparaffin are passed through a column having a fixed bed of an inertsupport. From the object thereof, the product must be a mixture ofvarious compounds. Thus, this method is not considered to pertain toselective alkylation. For example, in the case of trimethylpentane whichis the major product, the weight proportion is about 70% and theselectivity is low (U.S. Pat. No. 4,783,567 and No. 4,891,466).

U.S. Pat. No. 2,766,307, No. 2,803,682 and No. 2,803,683 and D. A.McCaulay and A. P. Lien, J. Am. Chem. Soc., 77, 1803 (1955) disclose amethod for producing alkylxylenes by ethylation or isopropylation ofmetaxylene. In the methods disclosed in the above patents and article,the catalyst system uses HF and BF₃ at the same time. Further, HF isused in an amount of 10 to 20 moles per mole of the raw materialsubstituted aromatic compound, which is much greater than that in thepresent invention. Thus, a problem is caused that the efficiency of theseparation and purification of HF used as the catalyst and the desiredproduct is low.

As an alkylation method using other acids, there may be mentioned fixedbed alkylation using a fluorinated sulfonic acid catalyst and reactionusing a zeolite catalyst (JP-A-Hei 09-2982). However, in the exampleusing a fluorinated sulfonic acid catalyst, the conversion of the rawmaterial aromatic compound is not satisfactory (about 30%). Further, themethod has a problem with respect to the selectivity, since branchedalkylated products and polyalkylated products are produced. A methoddisclosed in JP-A-2000-297049 and JP-A-2002-20325 uses zeolitecatalysts. While the method is excellent with respect to easiness inseparation of the product from the catalyst, polyalkylated products areby-produced in an amount of 10% or more. Additionally, the catalyst isexpensive.

DISCLOSURE OF THE INVENTION

In the above circumstance, it is an object of the present invention toprovide a process for producing an alkyl aromatic compound havingsubstituents at the 3- and 5-positions by alkylation of an aromaticcompound having two substituents at the meta positions, which is high inthe yield of and in the selectivity to the desired compound, whichpermits recovery and recycling of the catalyst and which can beindustrially practiced.

The present inventors have made earnest study in view of the foregoingcircumstance and have found that the desired alkyl aromatic compoundhaving substituents at the 3- and 5-positions can be obtained in astable manner with a high yield and a high selectivity under mild andsimple reaction conditions by alkylating an aromatic compound having twosubstituents at the meta positions with an olefin having 2 to 4 carbonatoms in the presence of a Broensted catalyst such as HF, followed byaddition of a Lewis acid such as BF₃ and permitting intramolecularisomerization to proceed. The present invention has been completed bythe above finding.

Thus, the present invention provides the following process for producingan alkyl aromatic compound.

1. A process for producing an alkyl aromatic compound represented by thegeneral formula (2), characterized in that an aromatic compoundrepresented by the general formula (1) is alkylated with an olefinhaving 2 to 4 carbon atoms in the presence of a Broensted acid, and inthat the resulting mixture is subsequently added with a Lewis acid andis subjected to isomerization in the copresence of the Broensted acidand the Lewis acid.

wherein R¹ and R² each independently represent an alkyl group, aperfluoroalkyl group, a halogen atom, a nitro group or an alkyloxy oraryloxy group which may have a substituent, X represents a hydrogenatom, an alkyl group, an aryl group, a perfluoroalkyl group, a halogenatom, a nitro group or an alkyloxy or aryloxy group which may have asubstituent, or X may be taken in combination with one or both of theadjacent groups R¹ and R² to represent a cycling structure which mayhave a substituent, and R represents an ethyl group, an isopropyl group,a sec-butyl group or a tert-butyl group.

2. A process for producing an alkyl aromatic compound as recited in 1above, in which the reaction of the aromatic compound represented by thegeneral formula (1) with the olefin in the presence of a Broensted acidis performed with a molar ratio of the Broensted acid to the aromaticcompound being 1 or more.

3. A process for producing an alkyl aromatic compound as recited in 1 or2 above, in which the reaction of the aromatic compound represented bythe general formula (1) with the olefin in the presence of a Broenstedacid is performed at a temperature lower than 50° C. but not lower than−30° C.

4. A process for producing an alkyl aromatic compound as recited in anyone of 1 through 3 above, in which the isomerization in the copresenceof the Lewis acid and the Broensted acid after the reaction of thearomatic compound represented by the general formula (1) with the olefinin the presence of a Broensted acid is performed with a molar ratio ofthe Lewis acid to the aromatic compound represented by the generalformula (1) being 0.5 or more.

5. A process for producing an alkyl aromatic compound as recited in anyone of 1 through 4 above, in which the isomerization in the copresenceof the Lewis acid and the Broensted acid after the reaction of thearomatic compound represented by the general formula (1) with the olefinin the presence of a Broensted acid is performed at a temperature lowerthan 50° C. but not lower than −30° C.

6. A process for producing an alkyl aromatic compound as recited in anyone of 1 through 5 above, in which the Broensted acid is HF and theLewis acid is BF₃.

7. A process for producing an alkyl aromatic compound as recited in anyone of 1 through 6 above, in which the olefin having 2 to 4 carbon atomsis selected from the group consisting of ethylene, propylene, butylenesand isobutylene.

8. A process for producing an alkyl aromatic compound as recited in anyone of 1 through 7 above, in which R¹ and R² are each a methyl group andX is a hydrogen atom in the general formulas (1) and (2), and in whichR⁰ is an isopropyl group in the general formula (2).

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in detail below. In the presentinvention, the aromatic compound represented by the above generalformula (1) is first reacted with an olefin having 2 to 4 carbon atomsand serving as an alkylating agent in the presence of a Broensted acidsuch as HF to form an alkylated aromatic compound.

As the olefin having 2 to 4 carbon atoms, there may be mentionedethylene, propylene, butylenes, isobutylene, etc. It is preferred thatthe olefin be used in an amount of 0.5 to 1 mole per mole of thearomatic compound represented by the formula (1). The use of the olefinin an amount of 0.5 to 1 mole is industrially advantageous because theselectivity based on the olefin is good.

The Broensted acid used in the alkylation reaction is preferably HF forreasons of strong acidity, easiness in recovery and separation, andhomogeneity of the complex thereof with a Lewis acid. A Lewis acid whichforms a complex with HF hinders the alkylation reaction and, therefore,should not be used in the alkylation stage. The amount of HF must be atleast 1 mole, preferably 2 to 5 moles, per mole of the raw materialsubstituted aromatic compound.

The alkylation of the present invention is characterized by beingcarried out using only Broensted acid and differs from the conventionalmethod in which the alkylation is performed using, as a catalyst, acombination of a Lewis acid such as a Friedel-Crafts catalyst with aBroensted acid or using a Lewis acid by itself. As described previously,the coexistence of a Lewis acid such as BF₃ in the alkylation stage isnot desirable because the alkylation is prevented from proceeding.

The alkylation temperature is generally lower than 50° C. but not lowerthan −30° C., preferably not higher than 20° C. but not lower than −20°C. An alkylation temperature below 50° C. can prevent the polyalkylationfrom proceeding and can increase the selectivity of the desiredmonoalkylated product. Although the temperature below −30° C. does notbring about problems, it is not necessary to excessively performcooling. During the course of the alkylation, the temperatureoccasionally temporarily increases due to exotherm. If the temperatureis quickly lowered by cooling, such a temporary temperature increasebeyond the above temperature range is permissive.

In the above alkylation step, the alkylation selectively occurs at aspecific position of the ortho, meta or para position depending upon theeffect of the functional group (orientation) on the aromatic ring. Forinstance, the alkylation of metaxylene with propylene in the presence ofan HF catalyst gives mainly 2,4-dimethlcumene.

Next, to the same reaction vessel, a Lewis acid such as BF₃ is fed sothat isomerization reaction occurs to obtain the compound represented bythe general formula (2) as a result of the intramoleculartransalkylation (isomerization). The intramolecular isomerization takesplace when the Broensted acid and the Lewis acid form a complex with thealkylated aromatic compound. The major product is a positional isomerwhich is more stable as a complex. Stated otherwise, the major productis an alkyl aromatic compound which has an increased basicity. Thus, theend product having a composition different from the thermodynamicallyequilibrium composition is obtained. For instance, 2,4-dimethylcumeneproduced by the alkylation of metaxylene with propylene in the presenceof an HF catalyst undergoes an isomerization reaction in the copresenceof HF and BF₃ to give 3,5-dimethylcumene. The above reaction, such asthe alkylation of metaxylene with propylene which results in theformation of 3,5-dimethylcumene, hardly proceeds, when the catalyst usedin the isomerization reaction is HF alone or BF₃ alone, or when HF andBF₃ coexist from the start of the initial alkylation stage.

The amount of BF₃ is preferably at least 0.5 mole per mole of thestarting aromatic compound. The reaction temperature may be the same asthat in the alkylation reaction and generally lower than 50° C. but notlower than −30° C., preferably not higher than 20° C. but not lower than−20° C.

The catalysts HF and BF₃ used in the present invention may be separated,recovered and recycled and do not encounter a problem of disposal ofwaste catalysts which has conventionally involved aluminum chloride.Namely, HF and BF₃ after the reaction can be easily separated andrecovered by being brought into thermal contact with recirculatinghydrocarbons in a distillation column and can be recycled to thereaction system. Since the reaction temperature is so low in the presentinvention, corrosion of the apparatuses is not caused. Further, since HFand BF₃ used in the present invention have a high positionalselectivity, the separation and purification of the desired product donot require a separation step by distillation and are easier as comparedwith the reaction product obtained by using a solid acid or other Lewisacids. Accordingly, the process of the present invention is aneconomically excellent industrial process.

In the present invention, since a Broensted acid is used in thealkylation reaction and a Lewis acid is used in the isomerizationreaction, and, in particular, since HF is used as the Broensted acid andBF₃ is used as the Lewis acid, each of the reactions may be carried outin a suitable manner. The above method quite differs from theconventional alkylation by Friedel-Crafts reaction or an improved methodthereof.

That is, the process of the present invention is characterized by theuse of only Broensted acid for carrying out a step which corresponds tothe alkylation in the conventional method and by the formation of aBroensted acid-Lewis acid complex, such as HF-BF₃, for carrying out astep which corresponds to an isomerization reaction. Namely, the pointin time at which a Lewis acid such as BF₃ is added is delayed. Thus, thealkylation using the Broensted acid, such as HF, and the isomerizationusing the Broensted acid-Lewis acid complex, such as HF-BF₃, are allowedto proceed as if the both reactions were a single reaction. Further, thereactions may be performed in “one pot” without removing the catalyst orisolating the product by distillation halfway in the reaction.

As described in the foregoing, the process of the present invention isexcellent in the results of the reaction as compared with theconventional method and has a number of advantages in the process stepsand, therefore, is clearly distinct from the conventional method.

The present invention will be described in more detail below by way ofexamples. However, the present invention is not restricted by theseexamples in any way.

In the examples, the reaction results (yield and selectivity) are valueson the basis of propylene unless otherwise specifically noted.

EXAMPLE 1

In a Hastelloy C autoclave having an inside volume of 300 mL andequipped with an electromagnetic stirrer, a baffle plate, a gas blowingport and a liquid feed port, 20 g (0.19 mole) of metaxylene was charged,to which 18.8 g (0.94 mole) of anhydrous HF was slowly fed from theliquid feed port under a pressure. The contents were cooled to −10° C.Next, 7.9 g (0.19 mole) of propylene was gradually fed to the autoclavefrom the gas blowing port. After the completion of the feed, stirringwas started and continued for 30 minutes. Stirring was then stopped and25.5 g (0.38 mole) of BF₃ was gradually introduced into the autoclavefrom the gas blowing port. The temperature before the BF₃ feed was −15°C. After the completion of the BF₃ feed, the stirring was again startedand continued for 30 minutes. Then, the reaction was terminated.Thereafter, the reaction mixture was poured in an ice water. Extractionwas carried out using 80 g of toluene and the organic layer wasseparated. The aqueous layer was again extracted with 50 g of toluene.The two organic layers were combined and washed with an aqueous sodiumhydrogen carbonate solution and then with purified water. The productwas analyzed by gas chromatography. The yield of 3,5-dimethylcumene was64%, and the selectivity was 92%.

EXAMPLE 2

A reaction was carried out using a Hastelloy C autoclave having aninside volume of 6,000 mL and equipped with an electromagnetic stirrer,a baffle plate, a gas blowing port and a liquid feed port in the samemanner as that in Example 1. For the reaction, 2,003 g (18.9 moles) ofmetaxylene, 943 g (47.1 moles) of anhydrous HF and 715 g (17.0 moles) ofpropylene were used. After the reaction was terminated, the reactionmixture was fed at a rate of 300 mL per hour together with 600 g perhour of benzene to a distillation column (column internal pressure: 0.38MPa, 122° C.) in which benzene was recirculated. A benzene solution of3,5-dimethylcumene was separated and collected from the bottom of thecolumn, while discharging BF₃ from the top and HF from a discharge portbelow the condenser. The benzene solution of 3,5-dimethylcumene obtainedfrom the bottom of the column was condensed using an evaporator and thendistilled (column internal pressure: 0.0133 MPa, stage number: 12, areflux ratio: 10) to obtain 1,925 g of desired 3,5-dimethylcumene(distillation temperature: 129° C.). The purity was 99.2% and isolationyield was 76%.

EXAMPLE 3

The reaction of Example 2 was carried out in the same manner.Thereafter, the reaction mixture was fed at a rate of 300 mL per hourtogether with 600 g per hour of benzene to a distillation column (columninternal pressure: 0.49 MPa, 136° C.) in which benzene was recirculated.A benzene solution of 3,5-dimethylcumene was separated and collectedfrom the bottom of the column, while discharging BF₃ from the top and HFfrom a discharge port below the condenser. The benzene solution of3,5-dimethylcumene obtained from the bottom of the column was condensedusing an evaporator and then distilled in the same manner as that inExample 2 to obtain 1,911 g of desired 3,5-dimethylcumene. The puritywas 99.0% and isolation yield was 76%.

EXAMPLE 4

The reaction of Example 2 was carried out in the same manner.Thereafter, the reaction mixture was fed at a rate of 140 mL per hourtogether with 430 g per hour of hexane to a distillation column (columninternal pressure: 0.38 MPa, 110° C.) in which hexane was recirculated.A hexane solution of 3,5-dimethylcumene was separated and collected fromthe bottom of the column, while discharging BF₃ from the top and HF froma discharge port below the condenser. The hexane solution of3,5-dimethylcumene obtained from the bottom of the column was condensedusing an evaporator and then distilled in the same manner as that inExample 2 to obtain 1,872 g of desired 3,5-dimethylcumene. The puritywas 98.7% and isolation yield was 74%.

EXAMPLE 5

Example 1 was repeated in the same manner as described except that thefeed amount of propylene was 4.0 g (0.09 mole). The product obtained wasanalyzed by gas chromatography to reveal that the yield of desired3,5-dimethylcumene was 74% and the selectivity was 91%. It isappreciated that the yield is improved by using propylene in an amountof 0.5 mole per mole of metaxylene as compared with the yield (64%)obtained by using propylene in an amount of 1 mole per mole ofmetaxylene.

EXAMPLE 6

Example 1 was repeated in the same manner as described except that theamount of HF was 9.4 g (0.47 mole) and the amount of BF₃ was 12.8 g(0.19 mole). The product obtained was analyzed by gas chromatography toreveal that the yield of desired 3,5-dimethylcumene was 70% and theselectivity was 94%. It is appreciated that the selectivity is improvedby using HF and BF₃ in amounts of 2.5 moles and 1 mole, respectively,per mole of metaxylene as compared with the selectivity (92%) obtainedby using HF and BF₃ in amounts of 5 moles and 2 moles, respectively, permole of metaxylene.

EXAMPLE 7

Example 1 was repeated in the same manner as described except thatpsudocumene was used in lieu of metaxylene. The product obtained wasanalyzed by gas chromatography to reveal that the yield of desired2,3,5-trimethylcumene was 74% based on the psudocumene and theselectivity was 99% based on the psudocumene.

COMPARATIVE EXAMPLE 1

Example 1 was repeated in the same manner as described except that BF₃was added before the feed of propylene. The product obtained wasanalyzed by gas chromatography to reveal that the yield of desired3,5-dimethylcumene was 9% and the selectivity was 99%. It is appreciatedthat, when BF₃ is added in the alkylation reaction stage, the yield isconsiderably low, although the selectivity is high.

COMPARATIVE EXAMPLES 2 to 7

Comparative Example 1 was repeated in the same manner as describedexcept that the amounts of HF and propylene (molar ratios relative tometaxylene) were changed. The yield of 3,5-dimethylcumene andselectivity are shown Table 1.

It is seen that, when BF₃ is added in the alkylation reaction stage,good results including the yield and selectivity are not obtained evenwhen the amounts of HF and propylene are changed. TABLE 1 Molar ratioemployed Reaction results Propylene/ Selectivity HF/metaxylenemetaxylene Yield (%) (%) Comparative 5 0.6 4 58 Example 2 Comparative 64 45 68 Example 3 Comparative 10 4 46 76 Example 4 Comparative 5 11 0 0Example 5 Comparative 5 4 19 47 Example 6 Comparative 20 4 48 50 Example7

COMPARATIVE EXAMPLE 8

Example 1 was repeated in the same manner as described except that BF₃was not added at all. The product obtained was analyzed by gaschromatography to reveal that the yield of desired 3,5-dimethylcumenewas 7% and the selectivity was 13% and the yield of 2,4-dimethylcumenewas 27%. It is appreciated that, when BF₃ is not added, theisomerization does not proceed.

COMPARATIVE EXAMPLE 9

Comparative Example 8 was repeated in the same manner as describedexcept that HF and propylene were used in amounts of 60 g (3.0 moles)and 32 g (0.75 mole), respectively. The product obtained was analyzed bygas chromatography to reveal that the yield of desired3,5-dimethylcumene was 0.2% and the selectivity was 0.2% and that theyield of 2,4-dimethylcumene was 0.5% and the yield ofdiisopropylmetaxylene was 70%. It is appreciated that, when the amountsof HF and propylene increase without using BF₃, the yield ofdi-substituted product considerably increases and the desired product ishardly obtained.

COMPARATIVE EXAMPLE 10

Comparative Example 1 was repeated in the same manner as describedexcept that, after HF, BF₃ and propylene had been entirely added, thereaction was performed for 6 hours. The product obtained was analyzed bygas chromatography to reveal that the yield of desired3,5-dimethylcumene was 1.1% and the selectivity was 27%. The yield of2,4-dimethylcumene was 0% and the yield of diisopropylmetaxylene was0.1%. From the fact that the alkylated products are scarcely obtainedeven when the reaction time is increased, it is seen that the alkylationreaction does not proceed in the presence of BF₃, but rather a stablemetaxylene/HF/BF₃ complex is formed.

COMPARATIVE EXAMPLE 11

Example 1 was repeated in the same manner as described except that HFwas not added at all and that the amount of BF₃ was changed to 19.2 g(0.28 mole) and the reaction time was changed to 30 minutes because noHF was added. The product obtained was analyzed by gas chromatography toreveal that the yield of desired 3,5-dimethylcumene was 0.9% and theselectivity was 2.4%. It is appreciated that when HF is not added, thealkylation reaction does not proceed.

INDUSTRIAL APPLICABILITY

According to the process of the present invention, in the production ofan alkyl aromatic compound which has substituents at the 3- and5-positions and which generally involves a difficulty in theintroduction into the aromatic nucleus, the desired alkyl aromaticcompound may be produced with high yield and high selectivity under mildand simple reaction conditions from a raw material aromatic compound.

The alkyl aromatic compounds produced by the process of the presentinvention are useful as intermediates for functional chemicals for usein pharmaceutical, agricultural and electronic materials.

With the method of the present invention, the catalyst used can berecovered and recycled. Thus, desired alkyl aromatic compounds may beobtained economically in an industrially advantageous manner whilereducing the load on the environment.

1. A process for producing an alkyl aromatic compound represented by the general formula (2), characterized in that an aromatic compound represented by the general formula (1) is alkylated with an olefin having 2 to 4 carbon atoms in the presence of a Broensted acid, and in that the resulting mixture is subsequently added with a Lewis acid and is subjected to isomerization in the copresence of the Broensted acid and the Lewis acid.

wherein R¹ and R² each independently represent an alkyl group, a perfluoroalkyl group, a halogen atom, a nitro group or an alkyloxy or aryloxy group which may have a substituent, X represents a hydrogen atom, an alkyl group, an aryl group, a perfluoroalkyl group, a halogen atom, a nitro group or an alkyloxy or aryloxy group which may have a substituent, or X may be taken in combination with one or both of the adjacent groups R¹ and R² to represent a cycling structure which may have a substituent, and R⁰ represents an ethyl group, an isopropyl group, a sec-butyl group or a tert-butyl group.
 2. A process for producing an alkyl aromatic compound as recited in claim 1, wherein the reaction of the aromatic compound represented by the general formula (1) with the olefin in the presence of a Broensted acid is performed with a molar ratio of the Broensted acid to the aromatic compound being 1 or more.
 3. A process for producing an alkyl aromatic compound as recited in claim 1, wherein the reaction of the aromatic compound represented by the general formula (1) with the olefin in the presence of a Broensted acid is performed at a temperature lower than 50° C. but not lower than −30° C.
 4. A process for producing an alkyl aromatic compound as recited in claim 1, wherein the isomerization in the copresence of the Lewis acid and the Broensted acid after the reaction of the aromatic compound represented by the general formula (1) with the olefin in the presence of a Broensted acid is performed with a molar ratio of the Lewis acid to the aromatic compound represented by the general formula (1) being 0.5 or more.
 5. A process for producing an alkyl aromatic compound as recited in claim 1, wherein the isomerization in the copresence of the Lewis acid and the Broensted acid after the reaction of the aromatic compound represented by the general formula (1) with the olefin in the presence of a Broensted acid is performed at a temperature lower than 50° C. but not lower than −30° C.
 6. A process for producing an alkyl aromatic compound as recited in claim 1, wherein the Broensted acid is HF and the Lewis acid is BF₃.
 7. A process for producing an alkyl aromatic compound as recited in claim 1, wherein the olefin having 2 to 4 carbon atoms is selected from the group consisting of ethylene, propylene, butylenes and isobutylene.
 8. A process for producing an alkyl aromatic compound as recited in claim 1, wherein R¹ and R² are each a methyl group and X is a hydrogen atom in the general formulas (1) and (2), and wherein R⁰ is an isopropyl group in the general formula (2).
 9. A process for producing an alkyl aromatic compound as recited in claim 2, wherein the reaction of the aromatic compound represented by the general formula (1) with the olefin in the presence of a Broensted acid is performed at a temperature lower than 50° C. but not lower than −30° C.
 10. A process for producing an alkyl aromatic compound as recited in claim 9, wherein the isomerization in the copresence of the Lewis acid and the Broensted acid after the reaction of the aromatic compound represented by the general formula (1) with the olefin in the presence of a Broensted acid is performed with a molar ratio of the Lewis acid to the aromatic compound represented by the general formula (1) being 0.5 or more.
 11. A process for producing an alkyl aromatic compound as recited in claim 10, wherein the isomerization in the copresence of the Lewis acid and the Broensted acid after the reaction of the aromatic compound represented by the general formula (1) with the olefin in the presence of a Broensted acid is performed at a temperature lower than 50° C. but not lower than −30° C.
 12. A process for producing an alkyl aromatic compound as recited in claim 11, wherein the Broensted acid is HF and the Lewis acid is BF₃.
 13. A process for producing an alkyl aromatic compound as recited in claim 12, wherein the olefin having 2 to 4 carbon atoms is selected from the group consisting of ethylene, propylene, butylenes and isobutylene.
 14. A process for producing an alkyl aromatic compound as recited in claim 13, wherein R¹ and R² are each a methyl group and X is a hydrogen atom in the general formulas (1) and (2), and wherein R⁰ is an isopropyl group in the general formula (2). 